Power supply system, power sourcing equipment, and Ethernet Y cable

ABSTRACT

A power sourcing equipment is provided. The power sourcing equipment is connected to an Ethernet cable. The power sourcing equipment includes a switching circuit, a power circuit, and a detection circuit. The power circuit is coupled to a power supply output terminal via the switching circuit. The detection circuit is configured to control a state of the switching circuit according to a first resistance between a first pin and a second pin of the Ethernet cable.

This application is a divisional application of U.S. patent applicationSer. No. 14/931,894, filed Nov. 4, 2015, now U.S. Pat. No. 9,973,343,which claims the benefits of People's Republic of China applicationSerial No. 201510166079.X, filed Apr. 9, 2015, U.S. provisionalapplication Ser. No. 62/189,260, filed Jul. 7, 2015 and People'sRepublic of China application Serial No. 201510489557.0, filed Aug. 11,2015, the subject matters of which are incorporated herein by reference.

BACKGROUND

Field of the Invention

The disclosure relates in general to a power sourcing equipment and apower supply system, and more particularly to a power sourcing equipmentand a power supply system where power is supplied via an Ethernet cable.

Related Art

Electronic devices need power to function properly, and so do thenetwork devices. Assume that a local network device, such as an Ethernetswitch, is connected to three remote network devices, such as wirelessnetwork base stations, four power supplies are required to make thislocal area network work. However, it may be difficult for networkdevices to be plugged into a mains socket if the network devices arelocated outdoors, on the roof, or on an enclosing wall of the house.

In the circumstances mentioned above, it may be better to supply powerto a network device through an Ethernet cable.

SUMMARY

The disclosure is directed to a power supply system, a power sourcingequipment (PSE), and an Ethernet Y cable. One of the advantages of thepower supply system is that the PSE automatically detects a powereddevice (PD) to determine whether or not power is supplied to the PD.

According to one embodiment of the invention, a power sourcing equipmentis provided. The power sourcing equipment is connected to an Ethernetcable. The power sourcing equipment includes a switching circuit, apower circuit, and a detection circuit. The power circuit is coupled toa power supply output terminal via the switching circuit. The detectioncircuit is configured to control a state of the switching circuitaccording to a first resistance between a first pin and a second pin ofthe Ethernet cable.

According to one embodiment of the invention, a power supply system isprovided. The power supply system includes an Ethernet cable, a powersourcing equipment, and a powered device. The power sourcing equipmentincludes a switching circuit, a power circuit, and a detection circuit.The power circuit is coupled to a power supply output terminal via theswitching circuit. The detection circuit is configured to control astate of the switching circuit according to a first resistance between afirst pin and a second pin of the Ethernet cable. The powered device isconnected to the power sourcing equipment via the Ethernet cable. Thepowered device makes the first pin of the Ethernet cable connected tothe second pin of the Ethernet cable.

According to one embodiment of the invention, a power supply system isprovided. The power supply system includes an Ethernet cable, a powersourcing equipment, and a powered device. The power sourcing equipmentincludes a switching circuit, a power circuit, and a detection circuit.The power circuit is coupled to a power supply output terminal via theswitching circuit. The detection circuit is configured to control astate of the switching circuit according to a first resistance between afirst pin and a second pin of the Ethernet cable. The powered device isconnected to the power sourcing equipment via the Ethernet cable. Thepowered device makes the first pin of the Ethernet cable connected tothe second pin of the Ethernet cable. The powered device includes aninternal resistor, which is disposed between the third pin and thefourth pin of the Ethernet cable.

According to one embodiment of the invention, an Ethernet Y cable isprovided. The Ethernet Y cable has a first terminal, a second terminal,and a third terminal. Each of the first, second, and third terminalsincludes a first pin, a second pin, a third pin, and a fourth pin. TheEthernet Y cable includes a first capacitor, a second capacitor, a thirdcapacitor, a fourth capacitor, and a first inductor. The first capacitorconnects the first pin of the first terminal to the first pin of thethird terminal. The second capacitor connects the second pin of thefirst terminal to the second pin of the third terminal. The thirdcapacitor connects the third pin of the first terminal to the third pinof the third terminal. The fourth capacitor connects the fourth pin ofthe first terminal to the fourth pin of the third terminal and the thirdpin of the second terminal. The first inductor connects the first pin ofthe second terminal to the first pin of the third terminal. The secondpin of the second terminal is connected to the fourth pin of the secondterminal.

According to one embodiment of the invention, an Ethernet Y cable isprovided. The Ethernet Y cable has a first terminal, a second terminal,and a third terminal. Each of the first, second, and third terminalsincludes a first pin, a second pin, a third pin, and a fourth pin. Thethird terminal further includes a fifth pin and a sixth pin. TheEthernet Y cable includes a first capacitor, a second capacitor, a thirdcapacitor, a fourth capacitor, and a first inductor. The first capacitorconnects the first pin of the first terminal to the first pin of thethird terminal. The second capacitor connects the second pin of thefirst terminal to the second pin of the third terminal. The thirdcapacitor connects the third pin of the first terminal to the third pinof the third terminal. The fourth capacitor connects the fourth pin ofthe first terminal to the fourth pin of the third terminal and the thirdpin of the second terminal. The first inductor connects the first pin ofthe second terminal to the first pin of the third terminal. The secondpin of the second terminal is connected to the fifth pin of the thirdterminal, and the fourth pin of the second terminal is connected to thesixth pin of the third terminal.

The invention will become apparent from the following detaileddescription of the preferred but non-limiting embodiments. The followingdescription is made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram illustrating a power over Ethernet (PoE) system.

FIG. 2 shows a diagram of a power sourcing equipment according to oneembodiment of the invention.

FIG. 3 shows a diagram of a power supply system according to oneembodiment of the invention.

FIG. 4 shows a circuit diagram of an implementation of the powersourcing equipment according to one embodiment of the invention.

FIG. 5 shows a diagram of a power sourcing equipment according to oneembodiment of the invention.

FIG. 6 shows a diagram of a power supply system according to oneembodiment of the invention.

FIG. 7 shows a circuit diagram of an implementation of the powersourcing equipment according to one embodiment of the invention.

FIG. 8 shows a diagram illustrating a power supply system utilizing anEthernet Y cable according to one embodiment of the invention.

FIG. 9 shows a diagram of the Ethernet Y cable according to oneembodiment of the invention.

FIG. 10 shows a diagram of the Ethernet Y cable according to oneembodiment of the invention.

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

DETAILED DESCRIPTION

FIG. 1 shows a diagram illustrating a PoE system. The PSE 10 isconnected to the PD 12 via an Ethernet cable. For example, the PSE 10may be a network switch, a WiFi adapter, or similar equipment capable ofsupplying power. The PD 12 may be a network device, such as an InternetProtocol (IP) telephone, a wireless access point (AP), or an IP camera.The PSE 10 supplies power and transmits data to the PD 12 via theEthernet cable. The PD 12 may also transmit data to the PSE 10 via theEthernet cable.

The Ethernet cable may be a category 5 cable (CAT-5), a category 5enhanced cable (CAT-5e), or CAT-6. The Ethernet cable includes fourtwisted pairs with 8 pins. Each twisted pair transmits a differentialsignal. The Ethernet cable is illustrated as four twisted pairs inFIG. 1. As shown in FIG. 1, pin 1 is paired with pin 2 to transmit datawith differential signal (TX+, TX−), and pin 3 is paired with pin 6 toreceive data with differential signal (RX+, RX−). The other two twistedpairs are pin 4 paired with pin 5, and pin 7 paired with pin 8.

The PSE 10 includes a voltage source 101, which may provide a DC voltagegenerated by voltage transformation and regulation of an AC voltagesource from supply mains. The data input/output terminal of the PSE 10includes a differential signal pair of pin 1 and pin 2 and anotherdifferential signal pair of pin 3 and pin 6. The differential signal isgenerated by a center-tapped transformer. The voltage output of thevoltage source 101 is coupled to the center tap of the transformer as acommon mode signal. The PD 12 has corresponding connection points, pins1, 2, 3, 6 of the Ethernet cable, where center-tapped transformers aredisposed as well. Therefore power may be supplied to an internal load121 of the PD 12. As such, pins 1, 2, 3, 6 of the Ethernet cable areresponsible for not only transmitting data but also supplying power tothe PD 12.

If the PSE 10 unconditionally supplies power to a random deviceconnected via Ethernet to the PSE 10, there may be potential damage tothe connected device. In order to prevent such situation, the PSE 10 maybe appropriately designed to identify whether or not the connecteddevice is compatible (suitable for being supplied power). For example,the PSE 10 (such as a wireless adapter) may be designed to supply powerto a specific IP camera. When a laptop computer is connected to the PSE10 via a Ethernet cable, there may be data transmission on the Ethernetcable. However, the PSE 10 will not supply power to the laptop computer.Similarly, the PD 12 may also be appropriately designed such that the PD12 can be successfully identified as a compatible powered device whenbeing connected to the PSE 10.

FIG. 2 shows a diagram of a power sourcing equipment according to oneembodiment of the invention. The PSE 2 is connected to an Ethernetcable. The PSE 2 includes a switching circuit 20, a power circuit 22,and a detection circuit 24. The power circuit 22 is coupled to a powersupply output terminal V_(out) via the switching circuit 20. Thedetection circuit 24 is configured to control a state of the switchingcircuit 20 according to a first resistance R_(v) between a first pin P₁and a second pin P₂ of the Ethernet cable.

Please refer to FIG. 3 for the operation of the PSE 2. FIG. 3 shows adiagram of a power supply system according to one embodiment of theinvention. The power supply system S1 includes the PSE 2 as describedabove, an Ethernet cable 3, and a PD 4. The PD 4 is connected to the PSE2 via the Ethernet cable 3. The PD 4 makes the first pin P₁ of theEthernet cable 3 connected to the second pin P₂ of the Ethernet cable 3.For example, in the PD 4, the first pin P₁ is directly connected to thesecond pin P₂ such that these two pins are effectively shorted or nearlyshorted. The PSE 2 may be a wireless adapter, the PD 4 may be an IPcamera, and the Ethernet cable 3 may be equipped with RJ45 connectorshaving eight pins.

The power circuit 22 may include a voltage transformer coupled to the ACsupply mains to provide a DC voltage, such as DC 12V or 48V. The stateof the switching circuit 20 is switched between an on state and an offstate to control whether or not the power circuit 22 provides power tothe power supply output terminal V_(out). The power supply outputterminal V_(out) is for example the center tap of the transformer asshown in FIG. 1. Therefore the switching circuit 20 controls whether ornot the PSE 2 supplies power to the PD 4 via the Ethernet cable 3. Thestate of the switching circuit 20 is controlled by the first resistanceR_(v) between the first pin P₁ and the second pin P₂ of the Ethernetcable 3. The first resistance R_(v) is detected by the detection circuit24.

When the first pin P₁ and the second pin P₂ are open circuited, forexample, there is no powered device being connected, the firstresistance R_(v) is an extremely large value. The detection circuit 24turns off the switching circuit 20. In other words, the switchingcircuit 20 is in the off state, and the PSE 2 does not supply power.

When there is another device different from the PD 4 connected to theEthernet cable 3, the detection circuit 24 detects the first resistanceR_(v) between the first pin P₁ and the second pin P₂. The firstresistance R_(v) may be caused by an internal resistance of thisconnected device. When the first resistance R_(v) is greater than orequal to a threshold resistance R_(th), the connected device isdetermined to be an incompatible device. The switching circuit 20 is inthe off state.

When the first resistance R_(v) is less than the threshold resistanceR_(th), the detection circuit 24 turns on the switching circuit 20. Theswitching circuit 20 is in the on state, and thus the PSE 2 suppliespower to the PD 4 via the Ethernet cable 3. One such example is shown inFIG. 3, the PD 4 makes the first pin P1 connected to the second pin P2.The first resistance R_(v) detected by the detection circuit 24 may bevery small (only the resistance on the Ethernet cable 3).

Refer to the PoE system shown in FIG. 1. Because pins 4, 5, 7, 8 of theEthernet cable are not designated to any specific use, pins 4, 5, 7, 8may be utilized to detect the first resistance R_(v). The first pin P₁may be pin 4 or pin 5 in a twisted pair. The second pin P₂ may be pin 7or pin 8 in the other twisted pair.

The PSE 2 and the PD 4 may be designed to match each other. The PD 4makes the first pin P₁ connected to the second pin P₂ such that thefirst resistance R_(v) detected by the detection circuit 24 is less thana threshold resistance R_(th), and then the PSE 2 is able to supplypower to the PD 4. The threshold resistance R_(th) may be 25Ω, 50Ω, orother suitable values, depending on the design requirements. On theother hand, when another device (such as a laptop computer) other thanthe PD 4 is connected, because the first pin P₁ and the second pin P₂are not shorted in this connected device, the detection circuit 24 maydetect the first resistance R_(v) as 150Ω, which may be the resistancebetween pin 4 and pin 7 of this connected device. In such case the PSE 2does not supply power to prevent possible damage to this device causedby the unexpected power supply.

In PSE 2, the detection circuit 24 detects a resistance and controls thestate of the switching circuit 20 accordingly. There may be severalpossible implementations of the PSE 2. One exemplary circuit is givenbelow. However, the invention is not limited to this circuit structure.

FIG. 4 shows a circuit diagram of an implementation of the powersourcing equipment according to one embodiment of the invention. The PSE5 includes a switching circuit 50, a power circuit 52, and a detectioncircuit 54. The detection circuit 54 includes a transistor T₁ (such asNMOS), having a control terminal (such as gate), a first terminal (suchas drain), and a second terminal (such as source). The control terminalis coupled to the first pin P₁ and coupled to the power circuit 52 via aresistor R₁. The first terminal is coupled to the power circuit 52 via aresistor R₂. The second terminal is coupled to the second pin P₂.

The switching circuit 50 includes a transistor T₂ (such as NMOS) and atransistor T₃ (such as PMOS). The transistor T₂ has a control terminal(such as gate) coupled to the first terminal of the transistor T₁, afirst terminal (such as drain) coupled to the power circuit 52 via theresistor R₃, and a second terminal (such as source) coupled to thesecond terminal of the transistor T₁. The transistor T₃ has a controlterminal (such as gate) coupled to the first terminal of the transistorT₂, a first terminal (such as drain) coupled to the voltage supplyoutput terminal V_(out), and a second terminal (such as source) coupledto the power circuit 52.

For ease of understanding, the output voltage of the power circuit 52 isdefined as V_(cc) (such as +12V), and the voltage level at the secondpin P₂ is defined as the common ground. When the first pin P₁ and thesecond pin P₂ are open circuited, there is no current flowing throughthe resistor R₁, the voltage of the first pin P₁ is about V_(cc). Thetransistor T₁ is on, and hence the voltage at the control terminal ofthe transistor T₂ is pulled down, and the transistor T₂ is off. Thevoltage at the control terminal of the transistor T₃ is about V_(cc).The transistor T₃ is off, and the power circuit 52 does not supply powerto the power supply output terminal V_(out).

When there is a first resistance R_(v)=150Ω between the first pin P₁ andthe second pin P₂, the voltage V_(cc) output from the power circuit 52is divided by a voltage divider formed by the resistor R₁ (such as 1 KΩ)and the first resistance R_(v). The voltage at the first pin P₁ is stillsufficiently high to turn on the transistor T₁ because of the ratio ofthe resistor R₁ to the first resistance R_(v). As described above, thetransistor T₂ is off and the transistor T₃ is off. The power circuit 52does not supply power to the power supply output terminal V_(out).

When the PD 4 makes the first pin P₁ connected to the second pin P₂ (thefirst resistance R_(v)˜0Ω), the voltage at the first pin P₁ is close toground level, and hence the transistor T₁ is off. The voltage at thecontrol terminal of the transistor T₂ is pulled high to turn on thetransistor T₂. Then the voltage at the control terminal of thetransistor T₃ is pulled down to turn on the transistor T₃. The powercircuit 52 outputs voltage to the power supply output terminal V_(out),that is, the PSE 5 supplies power to the PD 4.

In this embodiment, the PSE 5 may further include a capacitor C₁. Thecapacitor C₁ prevents possible error, such as the transistor T₃ beingturned on shortly, when this circuit initially boots up.

The PSE 5 described above is just exemplary rather than limiting. Thetransistors T₁-T₃ may be replaced by any switching elements, includingBJT, MOSFET, CMOS, etc. The connection relationship between otherpassive elements, including capacitors and resistors, may also beadjusted according to the chosen switching elements and theirpolarities.

FIG. 5 shows a diagram of a power sourcing equipment according to oneembodiment of the invention. As compared to the PSE 2 shown in FIG. 2,the detection circuit 24′ further controls the state of the switchingcircuit 20 according to a second resistance R_(z) between the third pinP₃ and the fourth pin P₄ of the Ethernet cable.

The control of the state of the switching circuit 20 may be for example:when the first resistance R_(v) is not equal to the second resistanceR_(z) or when the difference between the first resistance R_(v) and thesecond resistance R_(z) is sufficiently large, the detection circuit 24′turns on the switching circuit 20. When the first resistance R_(v) isequal to or sufficiently close to the second resistance R_(z), thedetection circuit 24′ turns off the switching circuit 20.

When the first pin P₁ and the second pin P₂ are open circuited, and thethird pin P₃ and the fourth pin P₄ are open circuited, in other words,there is no powered device connected to the PSE 2′. The first resistanceR_(v) and the second resistance R_(z) are effectively both extremelylarge values. In this case the detection circuit 24′ detects that thefirst resistance R_(v) and the second resistance R_(z) are equal. Thusthe switching circuit 20 is off, the PSE 2′ does not supply power.Similarly, when the first resistance R_(v)=150Ω between the first pin P₁and the second pin P₂, and the second resistance R_(z)=150Ω between thethird pin P₃ and the fourth pin P₄, the detection circuit 24 also turnsthe switching circuit 20 off.

When the first pin P₁ and the second pin P₂ are nearly short circuited,the first resistance R_(v) is close to 0Ω. On the other hand, the secondresistance R_(z) between the third pin P₃ and the fourth pin P₄ islarge, for example, R=1 KΩ. The detection circuit 24′ detects that thefirst resistance R_(v) is not equal to the second resistance R_(z), andthus the switching circuit 20 is turned on. The PSE 2′ supplies powervia the Ethernet cable.

As shown in FIG. 1, pins 4, 5, 7, 8 of the Ethernet cable are notdesignated to specific use. In one embodiment, the first pin P1 may bepin 4 of the Ethernet cable. The second pin P2 may be pin 7 of theEthernet cable. The third pin P3 may be pin 5 of the Ethernet cable. Thefourth pin P4 may be pin 8 of the Ethernet cable. In other words, pins1, 2, 3, 6 are used for transmitting data and power, while pins 4, 5, 7,8 are used for detecting resistance to determine whether or not theconnected device is a compatible powered device.

FIG. 6 shows a diagram of a power supply system according to oneembodiment of the invention. The power supply system S2 includes a PSE2′, an Ethernet cable 3, and a PD 6. The PSE 2′ and the PD 6 may bedesigned to match each other. The PD 6 makes the first pin P₁ connectedto the second pin P₂ of the Ethernet cable 3. The PD 6 includes aninternal resistor R_(in). The internal resistor R_(in) is disposedbetween the third pin P₃ and the fourth pin P₄ of the Ethernet cable 3.When the PD 6 is connected to the PSE 2′ via the Ethernet cable 3, thedetection circuit 24′ detects that the first resistance R_(v)(˜0Ω) isnot equal to the second resistance R_(z)(˜R_(in)). Therefore the PSE 2′supplies power to the PD 6 via the Ethernet cable 3.

In PSE 2′, the detection circuit 24′ detects the first resistance R_(v)and the second resistance R_(z) to control the state of the switchingcircuit 20 in response to the detection result. There may be severalpossible implementations of the PSE 2′. One exemplary circuit is givenbelow. However, the invention is not limited to this circuit structure.

FIG. 7 shows a circuit diagram of an implementation of the powersourcing equipment according to one embodiment of the invention. The PSE7 includes a switching circuit 70, a power circuit 72, and a detectioncircuit 74. The power circuit 72 is capable of providing two differentvoltage levels, including V_(CC) (such as +12V) and V_(DD) (such as+3.3V). The voltage level V_(DD) may be the power supply for the digitallogic circuits inside the PSE 7. The detection circuit 74 detects afirst resistance R_(v) between the first pin P₁ and the second pin P₂,and also detects a second resistance R_(z) between the third pin P₃ andthe fourth pin P₄. The detection circuit 74 includes an XOR gate G₁.

The first resistance R_(v) between the first pin P₁ and the second pinP₂ affects the output state of the transistor T₄. The second resistanceR_(z) between the third pin P₃ and the fourth pin P₄ affects the outputstate of the transistor T₅. The operation of the transistors T₄ and T₅may be referred to the embodiment related to the PSE 5 and FIG. 4, andthus is not repeated here. When the first resistance R_(v) and thesecond resistance R_(z) produces the same effect to the output of thetransistors T₄ and T₅, the XOR gate G₁ outputs logic 0. Then thetransistors T₆ and T₇ are off, and power is not supplied to the powersupply output terminal V_(out). On the other hand, when the firstresistance R_(v) and the second resistance R_(z) produces differenteffect to the output of the transistors T₄ and T₅, the XOR gate G₁outputs logic 1. Then the transistors T₆ and T₇ are on, and power issupplied to the power supply output terminal V_(out).

The PSE 7 described above is just exemplary rather than limiting. Thetransistors T₄-T₇ may be replaced by any switching elements, includingBJT, MOSFET, CMOS, etc. In addition, the number of the switchingelements may also be increased or decreased according to the operatingenvironment and the design criteria. The connection relationship betweenother passive elements may also be adjusted according to the chosenswitching elements and their polarities.

The power sourcing equipment and the power supply system disclosedherein utilize an Ethernet cable to supply power. Therefore the locationthat the powered device may be installed becomes more flexible, withoutbeing restricted by the socket location. The PSE is able to determinewhether or not the connected PD is a compatible device by detecting aresistance. When the detected resistance is within a predeterminedrange, or when multiple detected resistances satisfy a specificcondition, power is supplied to the PD. As such, the PSE is capable ofselectively supplying power to the PD according to the pairingrelationship between the PSE and the PD. Power is supplied only when thePD is determined as a compatible device. Therefore possible damage canbe avoided when other incompatible devices are connected via theEthernet cable to the PSE. Furthermore, the PD may be successfullyidentified by the PSE by connecting two pins of the Ethernet cable orproviding different resistance values.

In addition, a simple yet efficient circuit design is provided in thedisclosure to detect resistance between the pins. Therefore noadditional microprocessor is required to determine the compatibility ofthe PD. The circuit structure proposed herein does not occupy muchhardware area and thus effectively deal with the pairing process betweenthe PSE and the PD to save production cost.

Since pins 4, 5, 7, 8 of the Ethernet cable that are not designated toany specific use are utilized to detect resistance, the connectionstructure of the Ethernet is not affected. As shown in FIG. 1, datatransmission and power supply may be accomplished by pins 1, 2, 3, 6.There is no need to modify the Ethernet connection architecture. Pins 4,5, 7, 8 are used for the pairing mechanism between the PSE and the PD toachieve selective power supply.

FIG. 8 shows a diagram illustrating a power supply system utilizing anEthernet Y cable according to one embodiment of the invention. In thepower supply system S3, the PD 4 is connected to the PSE 2 and a datasetup device 8 via the Ethernet Y cable 9. In such configuration, thePSE 2 supplies power to the PD 4, and the data setup device 8 is able totransmit data to the PD 4 via network connection. For example, the PD 4is an IP camera, and the data setup device 8 is a personal computer. TheIP camera is power supplied by the PSE 2 while being setup by thepersonal computer. The PD 4 (such as IP camera) is connected to the PSE2 (such as wireless adapter) and the data setup device 8 (such aspersonal computer) simultaneously. Examples of the Ethernet Y cable 9are described below.

FIG. 9 shows a diagram of the Ethernet Y cable 91 according to oneembodiment of the invention. The Ethernet Y cable 91 has a firstterminal, a second terminal, and a third terminal. As shown in FIG. 8,the first terminal may be connected to the data setup device 8, thesecond terminal may be connected to the PSE 2, and the third terminalmay be connected to the PD 4. In one embodiment, the first terminal is amale interface, the second terminal is a male interface, and the thirdterminal is a female interface. As such, there may be another Ethernetcable disposed between the PD 4 and the third terminal of the Ethernet Ycable 91. The Ethernet Y cable 91 may be shortened in this way, hencefacilitating ease of use and also reducing the production cost of theEthernet cable 91.

The first terminal includes a first pin P₁₁, a second pin P₁₂, a thirdpin P₁₃, and a fourth pin P₁₄. The second terminal includes a first pinP₂₁, a second pin P₂₂, a third pin P₂₃, and a fourth pin P₂₄. The thirdterminal includes a first pin P₃₁, a second pin P₃₂, a third pin P₃₃, afourth pin P₃₄, a fifth pin P₃₅, and a sixth pin P₃₆.

The Ethernet Y cable 91 includes a first capacitor C₁, a secondcapacitor C₂, a third capacitor C₃, a fourth capacitor C₄, and a firstinductor L₁. The first capacitor C₁ connects the first pin of the firstterminal P₁₁ to the first pin of the third terminal P₃₁. The secondcapacitor C₂ connects the second pin of the first terminal P₁₂ to thesecond pin of the third terminal P₃₂. The third capacitor C₃ connectsthe third pin of the first terminal P₁₃ to the third pin of the thirdterminal P₃₃. The fourth capacitor C₄ connects the fourth pin of thefirst terminal P₁₄ to the fourth pin of the third terminal P₃₄ and thethird pin of the second terminal P₂₃. The first inductor L₁ connects thefirst pin of the second terminal P₂₁ to the first pin of the thirdterminal P₃₁. The second pin of the second terminal P₂₂ is connected tothe fifth pin of the third terminal P₃₅, and the fourth pin of thesecond terminal P₂₄ is connected to the sixth pin of the third terminalP₃₆.

Data transmission is needed between the data setup device 8 and the PD4. Pin 1 and pin 2 of the Ethernet cable are used to transmit data withdifferential signal (TX+, TX−), and pin 3 and pin 6 are used to receivedata with differential signal (RX+, RX−). In one embodiment, the firstto the fourth pins of the first terminal may be pins 1, 2, 3, 6 of theEthernet cable respectively. The first to the fourth pins of the thirdterminal may also be pins 1, 2, 3, 6 of the Ethernet cable respectively.

As the power supply system S1 shown in FIG. 3, the PSE 2 detects theresistance between the first pin P₁ (pin 4 or pin 5 of the Ethernetcable) and the second pin P₂ (pin 7 or pin 8 of the Ethernet cable) todetermine whether or not to supply power to the PD 4. Therefore in theembodiment shown in FIG. 9, the first pin of the second terminal P₂₁ maybe pin 1 of the Ethernet cable, the second pin of the second terminalP₂₂ may be pin 4 or pin 5 of the Ethernet cable, the third pin of thesecond terminal P₂₃ may be pin 6 of the Ethernet cable, and the fourthpin of the second terminal P₂₄ may be pin 7 or pin 8 of the Ethernetcable. The fifth pin of the third terminal P₃₅ may be pin 4 or pin 5 ofthe Ethernet cable, and the sixth pin of the third terminal P₃₆ may bepin 7 or pin 8 of the Ethernet cable. As such, the PSE 2 connected tothe second terminal is able to determine whether or not to supply poweraccording to the resistance detected between the second pin P₂₂ and thefourth pin P₂₄. If the determination result is affirmative, power issupplied via the first pin P₂₁ and the third pin P₂₃ to the PD 4connected to the third terminal.

In the above embodiment, the PSE 2 at the second terminal supplies powervia pin 1 and pin 6 of the Ethernet cable to the PD 4 at the thirdterminal. However, the connection method is not limited thereto. Powermay also be supplied to the PD 4 via any following combination of pinsof the Ethernet cable: pin 1 and pin 3, pin 2 and pin 3, pin 2 and pin6. For example, when the PSE 2 supplies power via pin 2 and pin 3, thefirst pin of the second terminal P₂₁ is pin 2 of the Ethernet cable, andthe third pin of the second terminal P₂₃ is pin 3 of the Ethernet cable.The mapping of the other pins at the first terminal and the thirdterminal may be adjusted correspondingly. For example, the first to thefourth pins of the first and third terminals may be pins 2, 1, 6, 3 ofthe Ethernet cable respectively.

The first to the fourth capacitors C₁-C₄ are disposed on the connectionpaths between the first terminal and the third terminal, such that DCsignal may be isolated, and AC signal in a particular frequency band maypass through. The capacitors C₁-C₄ may be regarded as AC coupling and DCblocking capacitors. For example, the PSE 2 provides a DC voltage 12V asthe supply power for the PD 4. The data setup device 8 is not affectedby the DC voltage 12V because of the blocking effect of the first to thefourth capacitors C₁-C₄, preventing possible damage to the data setupdevice 8 caused by excess current. Additionally, data setup device 8 isable to transmit AC signal related to setup data to the PD 4 through thefirst to the fourth capacitors C₁-C₄.

The first inductor L1 is disposed on the connection path between thesecond terminal and the third terminal, such that DC signal may passthrough and AC signal may be isolated. Therefore the PSE 2 is able tosupply DC power to the PD 4. As for the AC signal related to setup rata,because the second terminal is effectively isolated, the PSE 2 does notaffect the data transmission between the data setup device 8 and the PD4.

The capacitance of the first to the fourth capacitors C₁-C₄ and theinductance of the first inductor L₁ depend on the frequency of thecontrol and data signal transmitted on the Ethernet cable in order togenerate the desired frequency response. In one embodiment, thecapacitance of the first to the fourth capacitors C₁-C₄ ranges from 0.1μF-0.2 μF, and the inductance of the first inductor L₁ ranges from 4μH-8 μH.

The Ethernet Y cable in this embodiment connects the PSE, the PD, andthe data setup device simultaneously. The PSE may supply power to the PDvia the Ethernet Y cable, and the data setup device may perform setupprocedure on the PD also via the Ethernet Y cable. Furthermore, becauseappropriate capacitors and inductors are disposed in the Ethernet Ycable, signals are blocked or allowed to pass based on the signalfrequency. Consequently, the power supply signal does not interfere withthe transmitted data signal.

By utilizing the Ethernet Y cable 91 in this embodiment, the PSE is ableto detect the resistance to determine whether or not the PD is acompatible device. Power is supplied to the PD only when the detectedresistance is in a particular range. This pairing mechanism achievesselective power supply to prevent possible damage to the PD caused byunexpected power supply.

Another Ethernet Y cable 92 is provided in this disclosure. The EthernetY cable 92 may be used in the circumstance where the PSE 2 does not needto detect the PD 4, for example, when used by a user who is familiarwith the operation or by a skilled technician. Other examples include afixed particular usage mode, such as being used in the installationstage of an IP camera. Under these circumstances the PSE 2 suppliespower to the PD 4 without detecting the resistance in the PD 4. Thecircuit as well as the pin count is therefore simplified in the EthernetY cable 92.

FIG. 10 shows a diagram of the Ethernet Y cable 92 according to oneembodiment of the invention. The second pin of the second terminal P₂₂is connected to the fourth pin of the second terminal P₂₄. The secondpin P₂₂ and the fourth pin P₂₄ of the second terminal are not connectedto the third terminal. When the second terminal of the Ethernet cable 92is connected to the PSE 2, the resistance detected by the PSE 2 would bevery small. The PSE 2 then determines to supply power to the PD 4. Poweris supplied via the first pin P₂₁ and the third pin P₂₃ of the secondterminal to the PD 4 connected to the third terminal.

As compared to the Ethernet Y cable 91 shown in FIG. 9, the hardwarewiring used by the Ethernet Y cable 92 is reduced, also the pin count ofthe third terminal is reduced. The circuit design of the Ethernet Ycable 92 is simplified to reduce the production cost.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodiments.It is intended that the specification and examples be considered asexemplary only, with a true scope of the disclosure being indicated bythe following claims and their equivalents.

What is claimed is:
 1. A power sourcing equipment to be connected to anEthernet cable, the power sourcing equipment comprising: a switchingcircuit; a power circuit, coupled to a power supply output terminal viathe switching circuit; and a detection circuit, configured to control astate of the switching circuit according to a first resistance between afirst pin and a second pin of the Ethernet cable.
 2. The power sourcingequipment according to claim 1, wherein the detection circuit isconfigured to turn on the switching circuit when the first resistance isless than a threshold resistance.
 3. The power sourcing equipmentaccording to claim 1, wherein the detection circuit is configured toturn off the switching circuit when the first resistance is greater thanor equal to a threshold resistance.
 4. The power sourcing equipmentaccording to claim 1, wherein the first pin is pin 4 or pin 5 of theEthernet cable, and the second pin is pin 7 or pin 8 of the Ethernetcable.
 5. The power sourcing equipment according to claim 1, wherein thedetection circuit is configured to control the state of the switchingcircuit according to a second resistance between a third pin and afourth pin of the Ethernet cable.
 6. The power sourcing equipmentaccording to claim 5, wherein the detection circuit is configured toturn on the switching circuit when the first resistance is not equal tothe second resistance.
 7. The power sourcing equipment according toclaim 5, wherein the first pin is pin 4 of the Ethernet cable, thesecond pin is pin 7 of the Ethernet cable, the third pin is pin 5 of theEthernet cable, and the fourth pin is pin 8 of the Ethernet cable.
 8. Apower supply system, comprising: an Ethernet cable; a power sourcingequipment, comprising; a switching circuit; a power circuit, coupled toa power supply output terminal via the switching circuit; and adetection circuit, configured to control a state of the switchingcircuit according to a first resistance between a first pin and a secondpin of the Ethernet cable; and a powered device, connected to the powersourcing equipment via the Ethernet cable, wherein the powered devicemakes the first pin of the Ethernet cable connected to the second pin ofthe Ethernet cable.
 9. The power supply system according to claim 8,wherein the first pin is pin 4 or pin 5 of the Ethernet cable, and thesecond pin is pin 7 or pin 8 of the Ethernet cable.
 10. A power supplysystem, comprising: an Ethernet cable; a power sourcing equipment,comprising; a switching circuit; a power circuit, coupled to a powersupply output terminal via the switching circuit; and a detectioncircuit, configured to control a state of the switching circuitaccording to a first resistance between a first pin and a second pin ofthe Ethernet cable and a second resistance between a third pin and afourth pin of the Ethernet cable; and a powered device, connected to thepower sourcing equipment via the Ethernet cable, wherein the powereddevice makes the first pin of the Ethernet cable connected to the secondpin of the Ethernet cable, and the powered device comprises an internalresistor, which is disposed between the third pin and the fourth pin ofthe Ethernet cable.
 11. The power supply system according to claim 10,wherein the first pin is pin 4 of the Ethernet cable, the second pin ispin 7 of the Ethernet cable, the third pin is pin 5 of the Ethernetcable, and the fourth pin is pin 8 of the Ethernet cable.